The two main types of cofactors are organic and inorganic cofactors. Examples of organic cofactors include heme and Flavin. Examples of inorganic cofactors include metal ions such as Mg2+, Zn2+, K+, and Mn2+. Organic cofactors can be further divided into coenzymes and prosthetic groups depending on how tightly they bind to an enzyme. Coenzymes are organic cofactors that bind loosely to enzymes. Prosthetic groups are cofactors that bind tightly to enzymes.